Flip chip light emitting diode devices having thinned or removed substrates

ABSTRACT

In a method for fabricating a flip-chip light emitting diode device, epitaxial layers ( 14, 114 ) are deposited on a growth substrate ( 16, 116 ) to produce an epitaxial wafer. A plurality of light emitting diode devices are fabricated on the epitaxial wafer. The epitaxial wafer is diced to generate a device die ( 10, 110 ). The device die ( 10, 110 ) is flip chip bonded to a mount ( 12, 112 ). The flip chip bonding includes securing the device die ( 10, 110 ) to the mount ( 12, 112 ) by bonding at least one electrode ( 20, 22, 120 ) of the device die ( 10, 110 ) to at least one bonding pad ( 26, 28, 126 ) of the mount ( 12, 112 ). Subsequent to the flip chip bonding, a thickness of the growth substrate ( 16, 116 ) of the device die ( 10, 110 ) is reduced.

This application claims the benefit of U.S. Provisional Application Ser.No. 60/490,761 filed on Jul. 29, 2003.

BACKGROUND

The present invention relates to the electronics arts. It is especiallyrelates to group III-nitride flip-chip bonded light emitting diodes forlighting applications, and will be described with particular referencethereto. However, the invention also finds application in conjunctionwith other types of flip-chip bonded light emitting diodes, and in otherflip-chip bonded epitaxial semiconductor devices such as vertical cavitysurface emitting laser diodes.

In the flip-chip mounting configuration, a light emitting diode with alight-transmissive substrate and front-side electrodes is bonded “facedown” to bonding bumps of a mount, that is, with the epitaxial layersproximate to the mount and the light-transmissive substrate distal fromthe mount. The flip-chip arrangement has a number of advantages,including improved thermal heat sinking due to the proximity of thefront-side active layers to the heat sinking substrate, and reduction ofelectrode shadowing losses.

In the flip-chip mounting configuration, light is extracted from thesubstrate side. For epitaxially grown light emitting diodes, the choicesfor substrate material can be highly restricted since the substrate isselected principally to provide a good base for the epitaxy. Thus, thesubstrate criteria include a narrow lattice constant range, asubstantially atomically flat surface for nucleation of epitaxy, thermalstability at epitaxial growth temperatures, chemical compatibility withthe epitaxial process, and so forth.

A problem can arise in the flip-chip configuration when the growthsubstrate is substantially light-absorbing over some or all of thespectral range of light emission. In this case, light extraction fromthe substrate is reduced due to light absorption losses in thesubstrate. Moreover, even if a suitable optically transparent substrateis available, such as is the case for group III-nitride light emittingdiodes which can be grown on a transparent sapphire growth substrate,reflection optical losses can occur at the interface between thesubstrate and the epitaxial layers due to an abrupt discontinuity inrefractive index.

A known approach for reducing these substrate-related optical losses isto transfer the epitaxial layers stack from the light-absorbing growthsubstrate wafer to an optically transparent wafer. Typically, thisinvolves intimately bonding the epitaxial layers stack to the opticallytransparent wafer, and then removing the growth substrate wafer byetching. After removal of the growth substrate, the epitaxial layersstack remains bonded to the transparent wafer, which is then processedto fabricate devices, and diced to separate individual light emittingdiode die. However, achieving intimate bonding between the epitaxiallayers stack and the transparent substrate over large areas isdifficult. Device yield can be compromised due to the formation of airbubbles or the presence of particles at the interface between theepitaxial layers stack and the transparent substrate during the bonding.Moreover, absent a close refractive index match between the epitaxiallayers stack and the transparent substrate, reflections at the interfacebetween the layers stack and the transparent wafer can introduce opticallosses.

Another approach is to temporarily secure the epitaxial layers stack toa temporary support wafer using an adhesive layer, followed by thinningof the growth substrate. The epitaxial layers stack, with the remainingthinned growth substrate adhering thereto, is then detached from thetemporary support wafer and processed and diced to produce lightemitting diode die. The light emitting diode die, which have thinnedsubstrates, are flip chip bonded to a mount. However, the epitaxiallayers stack and the remaining thinned growth substrate form a fragilestructure after growth substrate thinning. The fragility of this thinnedstructure complicates the further processing, dicing, and flip chipbonding, resulting in lowered device yield. Moreover, air bubbles,particles, or other imperfections in the adhesion between the temporarysupport wafer and the epitaxial layers stack can introduce localizeddamage to the thinned structure, also impacting device yield.

The present invention contemplates an improved apparatus and method thatovercomes the above-mentioned limitations and others.

BRIEF SUMMARY

According to one embodiment, a method is provided for fabricating aflip-chip light emitting diode device. Epitaxial layers are deposited ona growth substrate to produce an epitaxial wafer. A plurality of lightemitting diode devices are fabricated on the epitaxial wafer. Theepitaxial wafer is diced to generate a device die. The device die isflip chip bonded to a mount. The flip chip bonding includes securing thedevice die to the mount by bonding at least one electrode of the devicedie to at least one bonding pad of the mount. Subsequent to the flipchip bonding, a thickness of the growth substrate of the device die isreduced.

According to another embodiment, a method is provided for improvinglight emission of a flip-chip bonded light emitting diode device that isflip chip bonded to a mount. A growth substrate of the light emittingdiode device is thinned or removed. The growth substrate of theflip-chip bonded light emitting diode device is arranged distal from themount. The thinning or removing is performed while epitaxial layers ofthe light emitting diode device are flip chip bonded to the mount. Theflip chip bonding effects a securing of the light emitting diode deviceto the mount during the thinning or removing.

According to yet another embodiment, a flip-chip light emitting diodedevice is disclosed. A mount includes bonding bumps. A light emittingdiode device die has a device layers stack that is flip chip bonded tothe bonding bumps of the mount. An underfill material is arrangedbetween the light emitting diode device die and the mount. The underfillmaterial supports the light emitting diode device die and prevents thelight emitting diode device die from fracturing.

Numerous advantages and benefits of the present invention will becomeapparent to those of ordinary skill in the art upon reading andunderstanding the present specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements ofcomponents, and in various process operations and arrangements ofprocess operations. The drawings are only for purposes of illustratingpreferred embodiments and are not to be construed as limiting theinvention. In the cross-sectional views, layer thicknesses areexaggerated for visual clarity, and are therefore not drawn to scale.

FIG. 1A shows a cross-sectional view of two light emitting diode diceflip chip bonded to a mount.

FIG. 1B shows a cross-sectional view of the two light emitting diodedice flip chip bonded to the mount as in FIG. 1A, after thinning of thesubstrates of the two light emitting diode dice.

FIG. 2 plots calculated light extraction fraction values of a groupIII-nitride flip-chip light emitting diode die having a silicon carbidesubstrate, calculated as a function of substrate absorption coefficientand substrate thickness.

FIG. 3 shows a cross-sectional view of the two light emitting diode diceflip chip bonded to the mount as in FIG. 1A, after removal of thesubstrates of the two light emitting diode dice.

FIG. 4A shows a cross-sectional view of two light emitting diode dicehaving a vertical current flow geometry flip chip bonded to a mount,prior to substrate thinning and formation of a back-side electrode.

FIG. 4B shows a cross-sectional view of the two light emitting diodedice flip chip bonded to the mount as in FIG. 4A, after thinning of thesubstrates, formation of back-side electrodes, and wire-bonding of theback-side electrodes to wiring bonding pads of the mount.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1A, two exemplary flip chip bonded light emittingdiode device die 10 are shown mounted in flip-chip fashion on a mount12. Each exemplary light emitting diode device die 10 includes asemiconductor device layers stack 14 that is epitaxially deposited on agrowth substrate 16. The epitaxial device layers stack 14 defines alight emitting diode device such as a group III nitride ultraviolet orblue light emitting diode, a group III phosphide visible-emission lightemitting diode, a group III arsenide vertical cavity surface emittinglaser diode, or the like.

In FIG. 1A, the semiconductor layers stack 14 has two exemplary layerscorresponding to a simple p/n diode; however, those skilled in the artwill appreciate that more complex semiconductor layers stacks can beemployed. In a vertical cavity surface emitting laser diode, forexample, the layers stack can include dozens of layers that define Braggreflectors, claddings, and a complex multi-quantum well active region.For a group III nitride ultraviolet or blue light emitting diode with ap-on-n orientation, the layers stack typically includes an epitaxialgrowth buffer of aluminum nitride or another material, an n-type galliumnitride base layer, an active region of indium gallium nitride, a p-typegallium nitride layer, and optionally a contact layer formed on thep-type gallium nitride layer. Those skilled in the art can readilyconstruct other semiconductor epitaxial layers stacks that are suitablefor specific optical applications.

The growth substrate 16 is made of a crystalline material that issuitable for epitaxial growth of the selected semiconductor layers stack14. For group III nitride epitaxy, the growth substrate is suitablysilicon carbide (SiC; for example, conductive SiC, undoped 6H-SiC, orundoped 4H-SiC), gallium nitride, or sapphire. For group III phosphideepitaxy, the growth substrate is suitably gallium arsenide or indiumphosphide. For group III arsenide epitaxy, the substrate is suitablygallium arsenide. These examples are not exhaustive; rather, thoseskilled in the art can readily select a growth substrate having asuitable surface lattice constant, a large-area planar surface, andappropriate thermal and chemical characteristics for promoting highquality, preferably lattice-matched epitaxial growth of the selectedsemiconductor layers stack 14. Optionally, the growth substrate 16 isoff-cut relative to a principle crystal direction. For example, 4H-SiCsubstrates that are on-axis (that is, no offcut) or offcut at 4° or 8°are available from Cree Materials (Durham, N.C.).

Epitaxial deposition of the semiconductor layers stack 14 on theselected growth substrate 16 is preferably by metal-organic chemicalvapor deposition (MOCVD; also known in the art as organometallic vaporphase epitaxy, OMVPE, and similar nomenclatures), molecular beam epitaxy(MBE), liquid phase epitaxy (LPE), or another suitable epitaxial growthtechnique. As with the growth substrate 16, the choice of epitaxialgrowth technique is made based on the type of epitaxial layer stack 14that is to be grown.

The epitaxial deposition is performed over a large-area substrate wafer.For example, silicon carbide wafers for epitaxy are available asgenerally disk-shaped wafers of diameter about 5 cm to 8 cm in diameter.Gallium arsenide and sapphire are available as larger diameterdisk-shaped wafers. The large-area substrate wafer with the epitaxiallayers stack 14 deposited thereupon is referred to herein as anepitaxial wafer. The epitaxial wafer is processed using a suitablefabrication process including sub-processes such as wafer cleaningprocesses, lithography processes, etching processes, dielectricdeposition processes, metallization processes, and the like to define aplurality of light emitting diode devices on the wafer. In a typicalapproach, the fabrication process includes initial wafer cleaning,lithographic definition and etching of device mesas, and lithographicdefinition and formation of n-type and p-type electrodes.

With continuing reference to FIG. 1A, the light emitting diode devicedie 10 are lateral current flow geometry devices, and include a p-typeelectrode 20 disposed on the device mesa and an n-type electrode 22disposed in a field area off the device mesa. In this embodiment, bothelectrodes 20, 22 are front-side electrodes. Typically, the electrodes20, 22 are made of gold or have gold coatings for facilitatinglow-resistance electrical contact.

The mount 12 includes a first bonding pad 26 arranged to connect withthe p-type electrode 20, and a second bonding pad 28 arranged to connectwith the n-type electrode 22. A plurality of bonding bumps 30 arearranged on the bonding pads 26, 28. The light emitting diode device die10 are flip chip bonded to the bonding pads 26, 28 of the mount 12, andmore specifically bond to the bonding bumps 30. Flip chip bonding can beachieved by soldering, in which case the bonding bumps 30 are solderbumps. Alternatively, flip chip bonding can be achieved by thermosonicbonding, in which case the bumps are preferably gold-coated copper bumpsthat are bonded to the gold of the electrodes 20, 22 by a combination ofheating and injection of ultrasonic energy. Other bonding methods canalso be employed.

With continuing reference to FIG. 1A, the flip chip bonded lightemitting diode die 10 have substrates 16 that are relatively thick. Thegrowth substrate wafer, which is typically at least a few centimeters indiameter or other lateral dimension, is diced to generate the individuallight emitting diode die 10 that are flip chip bonded to the mount 12.Hence, the substrates 16 of FIG. 1A have a thickness d corresponding tothe thickness of the original growth substrate wafer. For example,standard disk-shaped silicon carbide wafers for group III-nitrideepitaxy available from Cree Materials (Durham, N.C.) have typical waferdiameters of around 5.0 cm to 7.6 cm, and have wafer thicknessesspecified as 254±25.4 microns.

Moreover, silicon carbide is absorbing for the ultraviolet to blue lightemission of typical group III-nitride light emitting diode devices. Inthe flip chip bonding arrangement, light extraction is typically throughthe substrate side, and is attenuated by substrate absorption. In FIG.1A, extracted light is indicated schematically by tapered arrows 34. Arapid tapering of the arrow 34 as it passes through the relatively thicklight absorbing substrate 16 is indicative of optical losses due tolight absorption. Although described with reference to a silicon carbidesubstrate, it will be appreciated that other substrates that areabsorbing for light emitted by the semiconductor layers stack willsimilarly absorb light and reduce the external light output of thedevice.

With continuing reference to FIG. 1A and with further reference to FIG.1B, the substrate 16 shown in FIG. 1A is thinned after the flip chipbonding to produce modified light emitting diode die 10′ that havethinned substrates 16′, as shown in FIG. 1B. The thinned substrate 16′has a thickness d′ indicated in FIG. 1B that is substantially less thanthe thickness d of the unthinned substrate 16. The substrate thinningcan be performed by mechanical lapping, mechanical polishing, mechanicalgrinding, or the like. In another approach, the wafer thinning isperformed by wet etching or dry chemical or plasma etching using asuitable etchant. In yet another approach, laser ablation is used tothin the substrate. The reduced thickness d′ of the thinned substrate16′ allows more light to exit the light emitting diode die 10′, asindicated by less tapered, that is, broader arrows 34′ shown in FIG. 1B.

A preferred amount of thinning, that is, a preferred final thickness d′,is determined based on several factors. As a light-absorbing substrateis thinned, it generally becomes more light transmissive. Hence, asmaller thickness d′ typically promotes light extraction. However, asmaller final thickness d′ implies a smaller tolerance in the thinningprocess. In other words, for a smaller final thickness d′, the substratethinning process should be more precisely controlled to avoid leavingtoo much substrate material, on the one hand, or removing too muchmaterial and possibly damaging the underlying epitaxial layers stack 14,on the other hand.

With reference to FIG. 2, calculated light extraction values for atypical group III-nitride device structure on silicon carbide substratesof different thicknesses and absorption characteristics is shown. In theplot of FIG. 2, the abscissa is the substrate thickness in microns, andthe ordinate is light extraction fraction. Calculations are shownrunning from a typical silicon carbide growth wafer thickness of 254microns down to a highly thinned substrate thickness of about 25.4microns. Several curves are shown, each corresponding to a differentsubstrate absorption coefficient α, ranging from α=0.0 cm⁻¹ to α=20.0cm⁻¹. Those skilled in the art will appreciate that the absorptioncoefficient is wavelength dependent, and in the case of silicon carbidealso depends upon the polymorph, doping, and other characteristics ofthe silicon carbide material. The range of absorption coefficientsplotted in FIG. 2 is representative of substrate absorptioncharacteristics for typical group III-nitride light emitting diodedevice emission wavelengths and for typical silicon carbide substratematerials.

With continuing reference to FIG. 2, for α=5.0 cm⁻¹, thinning from asubstrate thickness of 254 microns to a substrate thickness of 50.8microns provides a relative light extraction improvement of about 10.2%(from a light extraction fraction of 0.2224 to a light extraction of0.2451). For a higher absorbing substrate the improvement is larger. Forexample, in the case of α=20.0 cm⁻¹, the light extraction fraction is0.1212 for a 254 micron substrate, and increases to 0.1918 for a 25.4micron substrate. Thus, in the case of α=20.0 cm⁻¹, thinning from 254microns to 25.4 microns provides a relative light extraction improvementof about 58.3%.

With reference returning to FIGS. 1A and 1B, thinning the substrate 16after flip chip bonding, rather than before dicing as has been typicallydone in the past, can introduce mechanical stability difficulties,especially for thinned substrates 16′ having thicknesses d′ of about 50microns or less. Stresses introduced by the bonding or by the substratethinning process can result in some, most, or all of the light emittingdiode devices 10′ being operatively degraded or non-functional. Forexample, some, most, or all of the light emitting diode devices 10′ canbreak during the thinning process due to stresses introduced at thediscrete bonding areas corresponding to the bonding bumps 30. Suchstresses may be supportable by the light emitting diode die 10 due toits thick substrate 16 and corresponding mechanical robustness, but maybe unsupportable by the light emitting diode die 10′ because of thefragility of its thinned substrate 16′.

To mechanically support and stabilize the light emitting diode devicesduring and after thinning, an underfill material 38 is preferablydisposed between the light emitting diode device 10 and the mount 12prior to substrate thinning. The underfill material 38 provides adhesivebonding between the light emitting diode device 10, 10′ and the mount 12that helps secure the devices 10, 10′. The underfill material 38 alsoprovides mechanical support for the thinned light emitting diode device10′ to reduce a likelihood of cracking or other stress-related damage.The support provided by the underfill material 38 is distributed acrossthe area of the light emitting diode device 10, 10′ to provide supportat or proximate to localized stress regions such as at or around thebonding bumps 30.

The underfill material 38 preferably provides other benefits, such asprotection and encapsulation of the semiconductor layers stack 14 andelectrodes 20, 22. If the underfill material 38 is thermally conductive,it advantageously provides an additional heat sinking path.

To provide for the thinning of the substrate, the underfill material 38preferably substantially does not cover the substrate 16, although theunderfill material 38 optionally can come part-way up sides of thesubstrate 16. In some contemplated embodiments, the underfill materialdoes cover the substrate 16, and the excess material covering thesubstrate 16 is removed during the substrate thinning process. Theunderfill material 38 is suitably applied as a fluid and then cured ordried before or after bonding. The underfill material 38 is suitably anepoxy, silicone, photoresist, or other material that can be applied in aliquid or flowable form and then cured or dried. Although inclusion ofthe underfill material 38 is preferred, the underfill material 38 isoptionally omitted if the thickness d′ of the thinned substrate is aboveabout 50 microns, or if the epitaxial layers stack 14 is sufficientlymechanically strong to be resistant to stress-related damage.

In the case of group III-nitride light emitting diode devices that emitblue or ultraviolet light, a wavelength converting phosphor can beincorporated into the underfill material 38 to convert the blue orultraviolet light into white light or light having other selectedspectral characteristics. Such phosphor incorporation is most beneficialin devices that employ a lateral current flow geometry, such as thelight emitting diode device die 10, 10′, since in this geometry asubstantial amount of light leaks toward the mount 12 through sidewallsof the etched mesa.

With reference to FIG. 3, rather than thinning the substrate 16 of FIG.1A, the substrate 16 can be completely removed, as shown in FIG. 3, toproduce the modified flip chip light emitting diode die 10″. In the caseof a transparent substrate such as a sapphire substrate used in groupIII-nitride epitaxy, optical losses attributable to the substrate aredue to reflection losses rather than absorption losses. Hence, thesapphire should be entirely removed to obviate the reflection opticallosses. In one suitable embodiment, a chemical etching is used thatremoves the substrate material selectively over the material of theadjacent epitaxial layer. In this case, the epitaxial layer of theepitaxial layers stack 14 that is adjacent to the substrate 16 serves asan etch stop, and the chemical etching advantageously terminates orgreatly slows when it reaches the etch stop layer.

Typically, complete removal of the substrate 16 provides improved lightextraction efficiency compared with retaining the thinned substrate 16′.However, if the substrate 16′ provides good refractive index matching tothe outside ambient, the thinned substrate 16′ can provide betteroverall light extraction efficiency than is obtained with completesubstrate removal. Moreover, complete substrate removal leaves a layerof the epitaxial layers stack 14 exposed to the ambient. In certaincases, this may be undesirable. For example, in a group III-arsenidedevice grown on a gallium arsenide substrate, if the exposed epitaxiallayer has a high aluminum content, it is prone to oxidation. Thus, insuch a case it may be preferable to keep a thin portion of the galliumarsenide substrate to cap the high aluminum-content epitaxial layer.Still further, absent an etch stop layer or a thick non-critical baseepitaxial layer, complete removal of the substrate 16 involves veryprecise control of the etch process to avoid etching into and damagingthe thin epitaxial layers stack 14.

In the case of removal or substantial thinning of the substrate 16, theresultant light emitting diode device 10′, 10″ may be so fragile as tobe incapable of being a free-standing component. That is, in the case ofextreme thinning or removal of the substrate 16, the underfill material38 advantageously prevents fracture of the light emitting diode device10′, 10″. Whether or not the modified light emitting diode device 10′,10″ is so fragile that the underfill material 38 prevents its fracture,rather than merely providing additional mechanical support, depends uponthe thickness of the epitaxial layers stack 14, the thickness d′ of thethinned substrate 16′ in the case of incomplete substrate removal, andthe mechanical properties of the materials that make up the lightemitting diode device 10′, 10″.

With continuing reference to FIG. 3, an index-matching material, anepoxy lens, discrete microlens, or other optical element 42 can beapplied to the epitaxial layer stacks 14 after removal of the substrates16. In the case of an epoxy lens 42, the epoxy is typically applied inliquid or flowable form and then dried or cured. Although not shown, itwill be appreciated that such optical elements can also be disposed onthe thinned substrates 16′ of FIG. 1B.

With reference to FIG. 4A, an embodiment employing devices having avertical current flow geometry is described. Light emitting diode die100 are shown in FIG. 4A flip-chip bonded to a mount 112. The lightemitting diode die 100 have an epitaxial semiconductor device layersstack 114 disposed on a substrate 116. A first electrode 120 is formedon the device layers stack 114. Unlike the lateral current flow geometryof FIGS. 1A, 1B, and 3, only a single front-side electrode 120 is formedon the epitaxial layers stack 114. The first electrode 120 is flip-chipbonded to a first bonding pad 126 via bonding bumps 130. A secondbonding pad 128 is not connected to the light emitting diode die 100 byflip chip bonding. Thus, at the point in fabrication shown in FIG. 4A,the light emitting diode die 100 are inoperative since there is nosecond electrode or electrical input thereto to drive the diode device.

With continuing reference to FIG. 4A and with further reference to FIG.4B, an underfill material 138 is preferably disposed between the lightemitting device die 100 and the mount 112 to provide mechanical support,improved securing of the device die 100 to the mount 112, and to provideoptional encapsulation and improved heat sinking. The substrate 116shown in FIG. 4A is thinned by mechanical grinding, laser ablation, wetchemical etching, dry etching, or the like to produce the thinnedsubstrate 116′. A second electrode 122, which is a back-side electrode,is formed on the thinned substrate 116, which is an electricallyconductive substrate. In the illustrated embodiment, the secondelectrode 122 is a ring electrode that defines a central opticalaperture 140 of each modified light emitting diode die 100′. The secondelectrode 122 is electrically connected with the second bonding pad 128,which is a wiring bonding pad, by a wire bond 142. When energized by theelectrodes 120, 122 the modified light emitting diode die 100′ emitslight 134 passing through the thinned substrate 116′ within the opticalaperture 140.

In the exemplary embodiment of FIG. 4B, the thinned substrate 116′ iselectrically conductive to enable a vertical current flow configuration.If, however, the substrate is electrically insulating, for example asapphire substrate of a group III-nitride light emitting diode die, thenthe substrate can be completely removed analogously to the embodiment ofFIG. 3, followed by formation of the backside contact on a layer of thesemiconductor layers stack 114 that is exposed by the removal of thesubstrate 116.

By removing the substrate after flip chip bonding, a number ofadvantages are realized over past fabrication methods that performedwafer thinning prior to flip chip bonding. Fabrication processes formaking the individual light emitting diode device die are performed onan epitaxial wafer that has a thick substrate wafer. This avoids damageduring handling of thin-wafer devices, and thus improves device yield.Moreover, in the case of substrate removal by isotropic etching with anetch stop, performing such isotropic etching after dicing and flip-chipbonding allows the isotropic etch process to simultaneously removematerial from both the back and the sides of the substrate wafer 16,116. This can provide faster substrate removal, especially in the caseof small-area devices. Moreover, inclusion of a supportive underfillmaterial 38, 138 provides improved structural stability during and afterthe substrate thinning or removal process, again increasing yield. Incertain embodiments, the supportive underfill material 38, 138 preventsmechanical failure and enables substrate thinning or removal to producedevices that cannot be generated as free-standing components.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

1. A method for fabricating a flip-chip light emitting diode device, themethod including: depositing epitaxial layers on a growth substrate toproduce an epitaxial wafer; fabricating a plurality of light emittingdiode devices on the epitaxial wafer; dicing the epitaxial wafer togenerate a device die; flip chip bonding the device die to a mount, theflip chip bonding including securing the device die to the mount bybonding at least one electrode of the device die to at least one bondingpad of the mount; and subsequent to the flip chip bonding, reducing athickness of the growth substrate of the device die.
 2. The method asset forth in claim 1, wherein the reducing of a thickness of the growthsubstrate subsequent to the flip chip bonding includes: thinning thegrowth substrate subsequent to the flip chip bonding.
 3. The method asset forth in claim 1, wherein the reducing of a thickness of the growthsubstrate subsequent to the flip chip bonding includes: removing thegrowth substrate subsequent to the flip chip bonding.
 4. The method asset forth in claim 1, further including: disposing an underfill materialat least between the mount and the flip chip bonded device die.
 5. Themethod as set forth in claim 4, wherein the disposing of the underfillmaterial includes: disposing the underfill material on the mount priorto the flip chip bonding.
 6. The method as set forth in claim 4, whereinthe disposing of the underfill material includes: disposing theunderfill material after the flip chip bonding, the disposing of theunderfill material further securing the device die to the mount.
 7. Themethod as set forth in claim 4, further including: disposing a phosphorin the underfill material.
 8. The method as set forth in claim 4,wherein the underfill material is selected to have a thermal expansioncoefficient matching one of a thermal expansion coefficient of thedevice die, a thermal expansion coefficient of the mount, and a thermalexpansion coefficient value intermediate between the thermal expansioncoefficients of the device die and the mount.
 9. The method as set forthin claim 4, wherein the disposing an underfill material includes:disposing a fluid underfill material; and curing the fluid underfillmaterial.
 10. The method as set forth in claim 1, wherein the reducingof a thickness of the growth substrate includes: mechanically grindingaway at least a portion of the growth substrate.
 11. The method as setforth in claim 1, wherein the reducing of a thickness of the growthsubstrate includes: chemically etching the growth substrate using achemical etchant.
 12. The method as set forth in claim 11, wherein thechemical etching includes: selecting a chemical etchant that etches thegrowth substrate preferentially over an etch stop epitaxial layer of thedeposited epitaxial layers, whereby the chemical etching terminatessubstantially at the etch stop epitaxial layer.
 13. The method as setforth in claim 11, wherein the chemical etchant produces a substantiallyisotropic chemical etching that simultaneously removes material from atop and sides of the growth substrate.
 14. The method as set forth inclaim 13, the method further including: subsequent to the flip chipbonding and prior to the chemical etching, arranging an underfillmaterial to encapsulate the epitaxial layers while leaving the top andsides of the growth substrate unencapsulated, the substantiallyisotropic chemical etching being ineffective for etching theencapsulating underfill material.
 15. The method as set forth in claim1, wherein the reducing of a thickness of the growth substrate includes:thinning or removing the growth substrate by laser ablation.
 16. Themethod as set forth in claim 1, wherein the epitaxial layers define avertical cavity surface emitting laser diode.
 17. The method as setforth in claim 1, wherein the epitaxial layers include group III-nitridecompound semiconductor layers.
 18. The method as set forth in claim 17,wherein the growth substrate is a silicon carbide substrate.
 19. Themethod as set forth in claim 17, wherein the growth substrate is asapphire substrate, and the reducing of a thickness of the growthsubstrate includes removing the sapphire substrate.
 20. The method asset forth in claim 19, the method further including: subsequent to theremoving the growth substrate, forming a back-side electrode to anepitaxial layer exposed by the removing of the growth substrate.
 21. Amethod for fabricating a flip-chip light emitting diode device, themethod including: depositing epitaxial layers on a growth substrate toproduce an epitaxial wafer; fabricating a plurality of light emittingdiode devices on the epitaxial wafer; dicing the epitaxial wafer togenerate a device die; flip chip bonding the device die to a mount, theflip chip bonding including securing the device die to the mount bybonding at least one electrode of the device die to at least one bondingpad of the mount; subsequent to the flip chip bonding, reducing athickness of the growth substrate of the device die by one of thinningand removing the growth substrate; and subsequent to the thinning orremoving of the growth substrate, forming a back-side electrode to oneof the thinned growth substrate and an epitaxial layer exposed by theremoving of the growth substrate.
 22. The method as set forth in claim21, further including: electrically connecting the back-side electrodeto a wiring bonding pad of the mount.
 23. The method as set forth inclaim 21, wherein the epitaxial layers include group III-nitridecompound semiconductor layers, the growth substrate is a sapphiresubstrate, and the reciting of a thickness of the growth substrate byone of thinning and removing the growth substrate includes removing thesapphire substrate by application of a laser beam.
 24. A method forimproving light emission of a flip-chip bonded light emitting diodedevice that is flip chip bonded to a mount, the method including:thinning or removing a growth substrate of the light emitting diodedevice, the growth substrate of the flip-chip bonded light emittingdiode device being arranged distal from the mount, the thinning orremoving being performed while epitaxial layers of the light emittingdiode device are flip chip bonded to the mount, the flip chip bondingeffecting a securing of the light emitting diode device to the mountduring the thinning or removing.
 25. The method as set forth in claim24, the method further including: prior to the thinning or removing,disposing an adhesive underfill material between the mount and the lightemitting diode device, the adhesive underfill material adhesivelyfurther securing the light emitting diode device to the mount during thethinning or removing.
 26. The method as set forth in claim 25, whereinthe adhesive underfill material additionally protects the epitaxiallayers of the light emitting diode device during the thinning orremoving.